Evolution Autopilot unable to hold course in waves

[wstigg]

Hi Forum - Forgive me if this topic has been covered elsewhere. I searched for a bit but found nothing.

My new Evolution AP system (EV-1, ACU400, P70, rudder reference sensor, Type2 Linear drive) in concert with the rest of my ST60 instruments does a swell job holding course in flat water and in moderate waves. When reaching and running in a fresh breeze with waves over a couple of meters, however, the AP struggles. When the waves are over 4 meters, the system can hold a course +/- 25 degrees in leisure mode and +/- 35 degrees in performance mode. Odd that performance mode is worse than leisure.

I can hand steer in these conditions, holding a course of +/- 10 degrees, using very little rudder, but anticipating the waves and making small course corrections before the waves lift the stern and send us surfing down the hill with neutral rudder.

Leisure mode comes closest to hand-steering, but it is still using 3 times as much rudder. Cruising mode is more active on the helm and performance mode seems to be hunting all the time.

We are a Carl Schumacher designed, performance monohull sailboat, 48 feet x 30,000 lbs. In the problem conditions, we are moving at 10 - 11 knots and surging to 14K and up. Sail plan is well balanced.

All components are running latest software builds, except P70 which is at 3.05. (Differences between 3.05 and 3.07 don't appear to be significant to this issue.) ST60 boat-speed is calibrated and accurate.

I've been through the entire dockside setup and linearization process successfully. Deviation on EV! shows 7 degrees.

I have selected Vessel-Type = Sail. Should I try a different Vessel Type? If so, what type might offer good course-keeping?

It sure seems to me that with good rate-gyros sensing pitch, yaw, and roll, sooner than I can feel them, that the system should be able to steer as well as I can in these difficult conditions.

Any help/advice is welcome! Thanks, Willy

[Chuck - Raymarine - Moderator]

Welcome to the Raymarine Forum Willy,

Has a rudder reference transducer been installed and interfaced to the system?

[wstigg]

Hi Chuck - Thanks for prompt replyt!

Yes, new rudder reference sensor was included in my AP Kit. It's installed and seems to be working well, giving me the pretty green and red bars as the rudder swings back and forth. Also went through the dockside setup and linearization process twice: once when first installing the system and again after upgrading all the software. Forgot to mention that we're using a ST1 - STng converter to interface ST60 instruments with AP. Converter is running latest software as well.

Cheers, /willy

[Chuck - Raymarine - Moderator]

Willy,

The sea states which you are experiencing problems with may be exceeding the design for the Evolution autopilot, particularly for following seas.

There is very little you can do with an Evolution autopilot in way of adjustment. The only settings available to improve such performance would be Response, Rudder Damping and Vessel Hull type.

The important thing is to make sure the boat has the correct pilot and drive unit at the start and the pilot is set up correctly with regard to the drive type, vessel type and undertake the Dockside wizard. This will set the autopilot up for the boat type and steering characteristics. The pilot then knows the speed and up to what angle it can turn the helm. The set hard over time is important and is automatically set by the drive type and the helm angle.

The hard over time should be around 10 seconds or quicker. Too quick can cause helm instability and over activity. Too slow can cause under-steering and wandering. So with this boat it may be too slow. What is the hard over to hard over time for your autopilot? While slower response time may be alright in calmer weather, the helm needs to respond more quickly to the boat being pushed off course by the waves. Accordingly, should the hard over to hard over time be too slow, then the autopilot may not be capable of applying helm or counter rudder.

The vessel Hull type will make a difference as this sets the pilots characteristics to one of three boat models, for a mono sail boat this is only really two, Sail slow turn and Sail. You could try changing this setting to Sail as it will have an effect on the Gain and Counter rudder response.

Rudder Damping would help to stop over activity or s-ing ... I don't believe that this applicable.

The Pilot Response is the only adjustment you have while you are in Auto and it acts like a dead band. Leisure will open up the dead band and make the pilot less active and responsive to being off the auto course. If the sea is pushing the boat around you may not notice any difference in this setting. In Performance it will tighten up the response so should steer better but could make it too twitchy and have the adverse effect especially if the hard over to hard over time is too slow to keep up.

Again, performance under such sea states may exceed the design of the autopilot, but the above may help.

[wstigg]

Hi Chuck - Thank you for your detailed response!

It would be very disappointing to conclude that the Evolution AP system cannot handle the sea-state I'm encountering. These waves and conditions are quite modest compared to the conditions we encounter in the Southern Ocean. I researched this AP upgrade extensively and narrowed my selection to NKE and Ray, finally selecting Raymarine after conferring with your reps at the METS show in Amsterdam. Too early, methinks, to pull the plug on this AP, however.

I've been seeing my problems with vessel type set to Sail. I'll try Sail-Slow Turn to see if this helps. Two questions for now:

1. How should I check my hard-over time? Is this center-to-stop time? Or Starboard stop-to-port-stop time? How to check?

2. How do I adjust my rudder damping?

I'm happy to check my hard-over time and try Slow-Turn and/or play with rudder damping to get acceptable course-keeping performance.

Again, many thanks for your good help!

Cheers, Willy

[Chuck - Raymarine - Moderator]

Willy,

1) Hard over time (more correctly referred to as hard over to hard over time) is the time taken by the autopilot to shift the rudder from the lesser of full port or 30 degrees to port to the lesser of full starboard or 30 degrees to starboard. Please click here to view a FAQ addressing this subject.

2) Rudder Damping is adjusted via the command sequence MENU->SET-UP->AUTOPILOT CALIBRATION->DRIVE SETTINGS->RUDDER DAMPING.

[wstigg]

Thank you Chuck!

I'll check the hard-over-to-hard over time per your advice and experiment with rudder damping.

Will also try Sail-Slow Turn configuration.

Hopefully we'll find suitable conditions for testing on our way down the west coast of Mexico over the coming weeks/months.

I'll let you know how we get on.

Cheers, Willy SV Pazzo

[Chuck - Raymarine - Moderator]

You're welcome.

[wstigg]

Hi Chuck from about 10 miles off Baja. Sailing thru cell coverage so just wanted to touch base. If you prefer we can take this conversation off the forum. If so, best email on boat is [email protected]. This is our iridium email. [email protected] works as well.

Hard-over-to-hard-over time is about 11 or 12 seconds. This is based on doubling hard-over-to center time while tied to the dock. After AP passes center, correction pauses, I assume to give compass a chance to respond. Fastest helm motion is in performance mode. Leisure mode gives slowest time.

I haven't experimented, yet, with damping or alternate vessel type. However...

Yesterday's experience tells me I have something wrong in my installation.

We were sailing with asymmetrical spinnaker on 150 degrees apparent wind, 18 - 20 knots with seas about 1 meter. Even in these mild conditions, boat was swinging thru +/- 15 degrees (30 degrees full range) in Leisure mode and +/- 25 degrees in Performance mode. Course-keeping seems to be a couple degrees better when sailing in Vane mode than when in compass mode.

This course keeping is less than my venerable Autohelm 7000 could do. This leads me to think I have something wrong in my setup.

Will continue to experiment with rudder damping and vessel type as you suggest, but just wanted to share new info in case this gives you more ideas.

Not sure when I'll have internet connection again, so your patience, and your help, is hugely appreciated!! Cheers, Willy SV Pazzo

[wstigg]

Hi Chuck - Just went looking for Rudder damping. No find under DRIVE SETTINGS, where my only choices are: POWER STEER, RUDDER OFFSET, AND RUDDER LIMIT. I'm running software versions:
EV1 2.17
ACU 2.17
p70 3.05
Converter 2.01
Other hiding places for RUDDER DAMPING?

Cheers, /w